The present invention relates to a method for controlling clutch disengagement in a vehicle having an automated manual transmission comprising an electronically controlled clutch.
As is well known by persons skilled in the art of controlling clutch and gearbox in a vehicle having an automated manual transmission, there is a problem concerning clutch disengagement in panic brake situations, i.e. where an operator of the vehicle maneuvers a brake pedal in order to get an as fast vehicle stop as possible.
In vehicles having a manual transmission, the operator himself/herself controls the clutch disengagement responsive to present circumstances. For example, it is not very beneficial to disengage the clutch for light braking; on the contrary, by keeping the clutch and gearbox engaged, it is possible to let the engine absorb some of the brake energy; by letting the engine absorb energy, brake wear and risk for brake overheating could be reduced.
In some brake situations, it is however desired to have an as fast clutch disengagement as possible; this is desired e.g. in situations requiring a rapid braking of vehicle velocity; at a rapid braking of the vehicle, the engine rotation will have enough inertia to require brake force from the vehicle brakes, which is the opposite situation as compared to the earlier mentioned situation concerning engine braking.
For vehicles comprising an automated manual transmission, i.e. an electronically controlled clutch and gearbox, it is of course beneficial if the above mentioned features could be obtained, but since there is no clutch pedal in such vehicles, the information used to control the clutch must come from other sources.
Presently, this information comes mainly from wheel sensors sensing a rotational speed of the wheels. The signal from the wheel sensors is used to decide whether the clutch should be engaged/disengaged. There is however at least one problem connected with using wheel sensor signals to control clutch disengagement, namely that there is a time delay from actual brake pedal maneuvering and signal arrival. On a slippery surface, the engine may stall if the braking is so hard that the driven wheels are locked and the clutch is not disengaged fast enough. This delay might delay an optimum braking performance of the vehicle.
According to an aspect of the present invention, a method comprises the steps of:
i. sensing at least two brake pedal positions separated in time,
ii. performing a differentiation of the sensed brake pedal positions,
iii. comparing the result of the differentiation to a first predetermined threshold value, and
iv. controlling the clutch to disengage if the result of the differentiation represents a faster brake pedal application than a predetermined threshold value.
In a further development of the invention, the steps of:
v. continuously sensing brake pedal position,
vi. continuously comparing the sensed brake pedal position with a second predetermined threshold value, and
vii. controlling the clutch to disengage if the continuously sensed brake pedal position at any time exceeds the second predetermined value,
are added to the method according to the invention.
By the added steps v-vii, the clutch will disengage upon heavy braking, even if the actual brake application is slow.
In a preferred embodiment of the invention, the first predetermined threshold value represents a brake application rate of 15% of maximum applicable brake force in less than 0.1 second.
In another preferred embodiment, the second predetermined threshold value represents 30% of maximum applicable brake force.